This collaborative research project is designed to provide a physical and genetic map of the genome of Drosophila Melanogaster, using in situ hybridization of large DNA molecules cloned into yeast cells by means of yeast artificial chromosome (YAC) vectors. Preliminary experiments have yielded an initial YAC library containing Drosophila inserts of up to 140 kbp, some of which are presently being studied, and construction of a library with even larger inserts is in progress. Library construction has been carried out using a new YAC vector containing the ends of the transposable element P with an eye to P-element-mediated transformation of large molecules of DNA. The specific aims of the proposed research are to produce and characterize a Drosophila library with inserts averaging 165 kbp (ideally using a vector under construction which will allow easy production of RNA probes for in situ hybridization), to perform initial tests of the feasibility of transformation using YAC vectors, and (the main thrust of the proposed research) to determine the location of large-insert YAC clones in the Drosophila genome by means in situ hybridization to salivary gland chromosomes.